Pain in sickle cell disease is poorly recognized, measured, and treated. Although painful episodes are the most common reason sickle cell patients seek care, studies have seldom directly measured pain in detail. In studies to date, biological and demographic variables alone only partly explain the observed variance in painful episode frequency. Further, little is known about differences in pain responses including home management versus health care utilization. Aims of this cohort study are to measure the variability in pain and response to pain in sickle cell disease, and to build multivariate models to explain both patients' pain and their response to pain, especially, utilization of health care. The models' outcome variables will include mean pain, painful episodes, and various types of utilization episodes, including non-narcotic analgesic use, narcotic use, office visits, emergency department (ED visits, and hospitalization. An additional outcome will be the percentage of each patient's painful episodes that result in various types of utilization. Outcomes will be operationalized using daily pain diaries collected over 6 months. Reflecting on the prior 24 hours, patients will recall on an ordinal (0-9) scale maximum pain, distress, and disability, judge whether they were in a "crisis," and note pain locations andtheir various types of utilization. Daily pain intensity ratings will be transformed into pain episode counts using a formulaic threshold for a painful episode. The formula calculates each patient's threshold individually, based on his/her pain ratings. The models will measure the effect of several classes of explanatory variables (demographic, disease-related, psycho social, and readiness to utilize care), operationalized using primary data and validated instruments. Patients will be recruited from the central and Tidewater regions of Virginia, will undergo an initial survey battery, chart review, and a brief final survey, venipuncture and urine sampling, and complete pain diaries daily for 6 months. This study will advance knowledge of the etiology and influences on pain and pain response in sickle cell disease. By revealing potentially mutable explanatory variables, the study's results will suggest targets of biobehavioral treatment interventions. The study will also advance methods of measuring pain and pain response in sickle cell disease. By measuring pain directly, simultaneously with utilization, our results may validate or invalidate prior studies. Results of this study can be used to improve sickle cell pain diagnosis and treatment and to dispel myths about sickle cell pain.